from 类方法和静态方法和实例方法 import Date
class User:
    def __init__(self,birthday):
        self.__birthday=birthday

    def get_age(self):
        return 2020-self.__birthday.year

class Student(User):
    def __init__(self, birthday):
        self.__birthday = birthday

if __name__ == '__main__':
    user=User(Date(1990,2,1))
    print(user._User__birthday)
    print(user.get_age())